JP2007026682A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent invasion of moisture into the inside of a battery from a sealed part of the battery composed of a laminated film coating. <P>SOLUTION: A nonaqueous electrolyte secondary battery is made by using an adhesive in which a moisture absorbent is added to the inside adhesive layer to which a metallic layer and an inner side resin layer of the laminate film are pasted, and by housing battery elements with this laminate film as the outer packaging. At this time, as a moisture absorbent, sulfate or polyacrylic acid salt or the like is solely used or in assortment of two kinds or more, and added by 1% or more and 10% or less in the adhesive. Moreover, by making a thickness of the inside adhesive layer 1 μm or more and 5 μm or less, adhesiveness and a moisture invasion suppressing effect can be secured. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary electrolyte covered with a laminate film, and more particularly to a non-aqueous electrolyte secondary electrolyte capable of suppressing water intrusion into a battery.

  In recent years, many portable electronic devices such as a camera-integrated VTR (Videotape recorder), a mobile phone, or a laptop computer have appeared, and their size and weight have been reduced. Along with this, the demand for batteries used as power sources for portable electronic devices is growing rapidly, and the battery design is lighter, thinner, and more efficient in the storage space in devices to realize smaller and lighter devices. It is required to use. As a battery satisfying such requirements, a lithium ion battery having a large energy density and output density is most suitable.

  Among them, a battery having a high degree of freedom of shape, a thin and large area sheet type battery, a thin and small area card type battery, and the like are desired. However, in the conventional method using a metal can as an exterior, it is thin. It is difficult to produce a battery.

  In order to solve such problems, a battery using a substance having an adhesive action in an electrolytic solution or a gel electrolyte using a polymer has been studied. In these batteries, the electrode and the electrolyte are in close contact with each other, and the contact state can be maintained. This makes it possible to produce a thin battery using a film-like exterior material such as an aluminum laminate film.

  FIG. 1 shows the appearance of a battery using a laminate film as an exterior material. This battery 1 is produced by laminating a positive electrode and a negative electrode through a separator, covering a wound or zigzag battery element with a laminate film, and sealing the periphery of the battery element. The positive electrode terminal 2a and the negative electrode terminal 2b (hereinafter referred to as the metal terminal 2 as appropriate unless otherwise specified) are led out of the battery from the sealing portion of the laminate film.

  A laminate film used for a battery exterior is a multilayer film having moisture resistance and insulating properties, in which a metal layer is sandwiched between an outer resin layer and an inner resin layer made of a resin film. The metal layer plays the most important role in preventing moisture, oxygen and light from entering and protecting the contents. Aluminum (hereinafter referred to as “Al” as appropriate) is the most lightweight because of its lightness, extensibility, price, and ease of processing. Often used. Nylon or polyethylene terephthalate (hereinafter referred to as PET as appropriate) is used for the outer resin layer because of its beautiful appearance, toughness, and flexibility. In addition, since the inner resin layer is a portion that is melted and fused together by heat or ultrasonic waves, polyolefin is suitable, and unstretched polypropylene (hereinafter referred to as CPP as appropriate) is often used. An adhesive layer is provided between the metal layer and the outer resin layer and between the metal foil and the inner resin layer.

  However, such a battery structure has a problem that moisture easily enters from the sealing portion of the laminate film 4 from which the metal terminal 2 is derived. When the battery element is covered with the laminate film 4 and the periphery is sealed, the inner resin layer is melted and bonded, but the metal terminal 2 and the inner resin layer derived from the battery element have poor adhesion. For this reason, moisture easily enters through the interface between the metal terminal 2 and the laminate film 4. When moisture enters the battery, an undesirable electrochemical reaction is caused inside the battery to deteriorate battery characteristics, or gas is generated inside and the battery expands.

Therefore, Patent Document 1 and Patent Document 2 described below describe a method of improving sealing performance by interposing an auxiliary member between a metal terminal and a laminate film.
Japanese Patent Laid-Open No. 2001-277736 JP 2004-39358 A

  In Patent Document 1, at least a linear low density polyethylene film is attached to an inner resin layer of a laminate film via an adhesive, and an acid-modified linear low density polyethylene is used as an auxiliary member between the metal terminal and the laminate film. By interposing a film, sealing properties are improved. Since polyethylene has a slow moisture penetration among thermoplastic resins, it is possible to suppress moisture penetration through the auxiliary member.

  Moreover, in patent document 2, moisture penetration is suppressed by using the thermoplastic resin containing moisture absorbents, such as a silica gel, activated carbon, and a zeolite, for a part or whole of an auxiliary member. In Patent Document 2, as an example, in a portion near the end of the laminate film from which the metal terminal is derived, the dispersion of the moisture absorbent is suppressed in order to ensure the sealing property, and the moisture absorbent is more dispersed as it approaches the inside of the battery. An auxiliary member adapted to be described is described.

  However, moisture intrusion into the battery is not only from the interface portion between the laminate film and the metal terminal. In the laminate film, a resin layer is provided on both surfaces of the metal foil via an adhesive layer. However, since the moisture permeability of the adhesive layer is large, the problem of moisture infiltration still remains. For example, the adhesive layer has a water permeability of about 100 times that of CPP used for the inner resin layer.

  The amount of moisture intrusion is proportional to the intrusion path cross-sectional area (cross-sectional area of the adhesive layer) and inversely proportional to the intrusion path length (sealing width). Therefore, moisture penetration is suppressed by bonding without providing an adhesive layer between the metal layer and the inner resin layer, such as heating the resin to melt and bonding it to the metal foil, or bonding the resin film with a heat roller or the like. A method is conceivable. However, this method is not preferable because the manufacturing cost increases.

  Although a method of preventing moisture intrusion by enlarging the sealing width and enlarging the path length is conceivable, this method reduces the volume of the power generation element portion and hinders the increase in capacity of the battery.

  Accordingly, an object of the present invention is to provide a nonaqueous electrolyte secondary battery that is packaged with a laminate film having low moisture permeability and has little moisture penetration even with a narrow sealing width.

In order to solve the above-described problems, in the present invention, a battery element using an adhesive obtained by adding a moisture absorbent to an inner adhesive layer for adhering a metal layer and an inner resin layer of a laminate film, and using the laminate film as an exterior material To provide a non-aqueous electrolyte secondary battery. At this time, as the moisture absorbent, a sulfate represented by the general formula MSO ₄ or M ₂ SO ₄ (wherein M is selected from Na, K, Mg, Ca), or a general formula ( _{-CH 2 -CH (COOM) -.} ) polyacrylate (wherein represented by _n, M is the Na, K, Mg, selected from Ca), such as to select either singly or a reference, Add 1% to 10% in the adhesive.

  According to the present invention, moisture can be prevented from entering the battery via the adhesive layer between the metal layer and the inner resin layer of the laminate film, and gas generation inside the battery can be suppressed. Thereby, battery swelling can be prevented. Moreover, since the welding width of the laminate film can be reduced, the battery capacity can be improved.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. This time, a battery using a gel electrolyte will be described.

  FIG. 2 shows a configuration of a nonaqueous electrolyte battery 20 produced by applying the present invention. In the battery 20, the battery element 10 is accommodated in a recess 17 a formed in the laminate film 17 and is packaged, and the battery 20 is manufactured by sealing the periphery of the battery element 10. Hereinafter, the configuration of the battery element 10 will be described.

  FIG. 3 shows the structure of the battery element 10 accommodated in the laminate film 17. The battery element 10 includes a belt-like positive electrode 11, a separator 13 a, a belt-like negative electrode 12 disposed opposite to the positive electrode 11, and a separator 13 b, which are sequentially laminated and wound in the longitudinal direction. A gel electrolyte 14 is applied to both surfaces of the negative electrode 12. A positive electrode terminal 15a connected to the positive electrode 11 and a negative electrode terminal 15b connected to the negative electrode 12 are led out from the battery element 10 (hereinafter referred to as an electrode terminal 15 when not referring to a specific terminal). 15a and negative electrode terminal 15b have sealants 16a and 16b (hereinafter referred to as sealant 16 if a specific sealant is not indicated), which is a resin piece such as polyethylene (PE), in order to improve adhesiveness with laminate film 17 to be packaged later. Are referred to as appropriate).

[Positive electrode]
In the positive electrode, a positive electrode active material layer containing a positive electrode active material is formed on both surfaces of a positive electrode current collector. The positive electrode current collector is made of a metal foil such as an aluminum (Al) foil.

  The positive electrode active material layer includes, for example, a positive electrode active material, a conductive agent, and a binder. Here, the positive electrode active material, the conductive agent, the binder, and the solvent only have to be uniformly dispersed, and the mixing ratio is not limited.

As the positive electrode active material, a metal oxide, a metal sulfide, or a specific polymer can be used depending on the type of the target battery. For example, in the case of constituting a lithium ion battery, Li _x MO ₂ (wherein M represents one or more transition metals, and x varies depending on the charge / discharge state of the battery, and is usually 0.05 or more and 1.10 or less. ) And a composite oxide of lithium and transition metal. As the transition metal constituting the lithium composite oxide, cobalt (Co), Ni, manganese (Mn) or the like is used.

Specific examples of such a lithium composite oxide include LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiNi _y Co _1-y O ₂ (0 <y <1). A solid solution in which a part of the transition metal element is substituted with another element can also be used. Examples thereof include LiNi _0.5 Co _0.5 O ₂ and LiNi _0.8 Co _0.2 O ₂ . These lithium composite oxides can generate a high voltage and have an excellent energy density. _{Furthermore, TiS 2, MoS 2, NbSe} 2, V 2 O no lithium metal sulfides such as ₅ or may be used an oxide as the positive electrode active material. These positive electrode active materials may be used alone or in combination of two or more.

  As the conductive agent, for example, a carbon material such as carbon black or graphite is used. As the binder, for example, polyvinylidene fluoride, polytetrafluoroethylene, polyvinylidene fluoride, or the like is used. Moreover, as a solvent, N-methylpyrrolidone etc. are used, for example.

  The above-described positive electrode active material, binder, and conductive agent are uniformly mixed to form a positive electrode mixture, and this positive electrode mixture is dispersed in a solvent to form a slurry. Next, the slurry is uniformly applied on the positive electrode current collector by a doctor blade method or the like, and then dried at a high temperature to drive off the solvent, thereby forming the positive electrode active material layer 11b.

  The positive electrode 11 has a positive electrode terminal 15a connected to one end of the positive electrode current collector 11a by spot welding or ultrasonic welding. The positive electrode terminal 15a is preferably a metal foil or a mesh-like one, but there is no problem even if it is not metal as long as it is electrochemically and chemically stable and can conduct electricity. Examples of the material of the positive electrode terminal 15a include aluminum.

[Negative electrode]
In the negative electrode, a negative electrode active material layer containing a negative electrode active material is formed on both surfaces of a negative electrode current collector. The negative electrode current collector is made of a metal foil such as a copper (Cu) foil, a nickel foil, or a stainless steel foil.

  The negative electrode active material layer includes, for example, a negative electrode active material, a conductive agent if necessary, and a binder. These are uniformly mixed to form a negative electrode mixture, and this negative electrode mixture is dispersed in a solvent to form a slurry. Next, the slurry is uniformly applied on the negative electrode current collector by a doctor blade method or the like, dried at a high temperature, and the solvent is blown off to form a negative electrode active material layer. Here, the mixing ratio of the negative electrode active material, the conductive agent, the binder, and the solvent is not limited as in the positive electrode active material.

As the negative electrode active material, lithium metal, a lithium alloy, a carbon material that can be doped / undoped with lithium, or a composite material of a metal material and a carbon material is used. Specific examples of the carbon material that can be doped / undoped with lithium include graphite, non-graphitizable carbon, and graphitizable carbon. More specifically, pyrolytic carbons, cokes (pitch coke, needle coke, petroleum coke), graphites, glassy carbons, organic polymer compound fired bodies (phenolic resin, furan resin, etc.) at an appropriate temperature. Carbon materials such as those obtained by firing and carbonization), carbon fibers, activated carbon, and the like can be used. Furthermore, as a material capable of doping and dedoping lithium, a polymer such as polyacetylene or polypyrrole or an oxide such as SnO ₂ can be used.

  In addition, various kinds of metals can be used as materials capable of alloying lithium, but tin (Sn), cobalt (Co), indium (In), aluminum, silicon (Si), and alloys thereof can be used. Often used. When metallic lithium is used, it is not always necessary to use powder as a coating film with a binder, and a method of pressure bonding a rolled lithium metal foil to a current collector may be used.

  As the binder, for example, polyvinylidene fluoride, styrene butadiene rubber or the like is used. Moreover, as a solvent, N-methylpyrrolidone, methyl ethyl ketone, etc. are used, for example.

  The above-described negative electrode active material, binder, and conductive agent are uniformly mixed to form a negative electrode mixture, which is dispersed in a solvent to form a slurry. Subsequently, after apply | coating uniformly on a negative electrode electrical power collector by the method similar to a positive electrode, the negative electrode active material layer 12b is formed by making it dry at high temperature and flying a solvent.

  Similarly to the positive electrode 11, the negative electrode 12 has a negative electrode terminal 15b connected to one end of the current collector by spot welding or ultrasonic welding, and this negative electrode terminal 15b is electrochemically and chemically stable. There is no problem even if it is not metal as long as it can conduct electricity. Examples of the material of the negative electrode terminal 15b include copper and nickel.

  The positive electrode terminal 15a and the negative electrode terminal 15b are preferably derived from the same direction, but there is no problem regardless of the direction from which the positive terminal 15a and the negative electrode terminal 15b are derived as long as no short circuit occurs. Moreover, the connection location of the positive electrode terminal 15a and the negative electrode terminal 15b is not limited to the above example as long as electrical contact is established, and the attachment location and the attachment method are not limited to the above example.

[Electrolyte]
As the electrolytic solution, an electrolyte salt and an organic solvent that are generally used in lithium ion batteries can be used.

  Specific examples of the non-aqueous solvent include ethylene carbonate, propylene carbonate, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, ethyl propyl carbonate, or hydrogen of these carbonic acid esters to halogen. Examples include substituted solvents. One of these solvents may be used alone, or a plurality of these solvents may be mixed with a predetermined composition.

Moreover, as lithium salt, it is possible to use the material used for normal battery electrolyte solution. Specifically, LiCl, LiBr, LiI, LiClO ₃ , LiClO ₄ , LiBF ₄ , LiPF ₆ , LiNO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC (SO ₂ CF ₃ ) ₃ , LiAlCl ₄ , LiSiF _{6 and the} like can be mentioned, but LiPF ₆ and LiBF ₄ are preferable from the viewpoint of oxidation stability. These lithium salts may be used alone or in combination of two or more. There is no problem as long as the lithium salt can be dissolved in the above solvent, but the lithium ion concentration is 0.4 mol / kg or more and 2.0 mol / kg or less with respect to the non-aqueous solvent. Preferably there is.

  In the case of using a gel electrolyte, the above-described electrolytic solution is gelled with a matrix polymer. The matrix polymer is not particularly limited as long as it is compatible with a non-aqueous electrolyte obtained by dissolving the electrolyte salt in the non-aqueous solvent and can be gelled. Examples of such a matrix polymer include a polymer containing polyvinylidene fluoride, polyethylene oxide, polypropylene oxide, polyacrylonitrile, and polymethacrylonitrile in repeating units. Such a polymer may be used individually by 1 type, and may mix and use 2 or more types.

Among them, particularly preferred as the matrix polymer is polyvinylidene fluoride or a copolymer in which hexafluoropropylene is introduced at a ratio of 7.5% or less to polyvinylidene fluoride. Such polymers have a number average molecular weight in the range of 5.0 × 10 ⁵ to 7.0 × 10 ⁵ (500,000 to 700,000) or a weight average molecular weight of 2.1 × 10 ⁵ to 3. The range is 1 × 10 ⁵ (210,000-310,000), and the intrinsic viscosity is in the range of 1.7 to 2.1.

[Separator]
The separator is made of, for example, a porous film made of a polyolefin-based material such as polypropylene (PP) or polyethylene (PE), or a porous film made of an inorganic material such as a ceramic nonwoven fabric. A structure in which a porous film is laminated may be used. Among these, polyethylene and polypropylene porous films are the most effective.

  In general, the thickness of the separator is preferably 5 to 50 μm, more preferably 7 to 30 μm. If the separator is too thick, the amount of the active material filled decreases, the battery capacity decreases, and the ionic conductivity decreases and the current characteristics deteriorate. On the other hand, if the film is too thin, the mechanical strength of the film decreases.

[Production of battery]
The gel electrolyte solution prepared as described above is uniformly applied to the positive electrode 11 and the negative electrode 12 and impregnated in the positive electrode active material layer and the negative electrode active material layer, and then stored at room temperature or subjected to a drying process. A state electrolyte layer 14 is formed. Next, using the positive electrode 11 and the negative electrode 12 on which the gel electrolyte layer 14 is formed, the positive electrode 11, the separator 13 a, the negative electrode 12, and the separator 13 b are stacked and wound in this order to obtain the battery element 10.

  Next, the battery element 10 is accommodated in the recess 17 a of the laminate film 17 and is packaged. Here, the laminate film 17 used this time will be described in detail.

  FIG. 4 shows the configuration of the laminate film 17 used this time. In the laminate film 17, the metal layer 21 and the outer resin layer 22 are bonded by the outer adhesive layer 24, and the metal layer 21 and the inner resin layer 23 are bonded by the inner adhesive layer 25, and the total thickness is about 100 μm. It is. The metal layer 21, the outer resin layer 22, and the inner resin layer 23 can be manufactured using the aforementioned metal material and resin material, and the outer adhesive layer 24 and the inner adhesive layer 25 are, for example, polyurethane-based, acrylic-based, styrene-based, or the like. An adhesive conventionally used in the production of laminate films can be used.

  Here, in order to prevent moisture from entering the battery through the inner adhesive layer 25 provided between the metal layer 21 and the inner resin layer 23 this time, sulfate, polyacrylate, etc. A laminate film 17 is produced by dispersing one or more kinds of water absorbents having high hydration properties in the range of 1% or more and 10% or less.

  Specifically, sodium sulfate, potassium sulfate, magnesium sulfate, and calcium sulfate can be used as the sulfate, and polyacrylate includes sodium polyacrylate, potassium polyacrylate, magnesium polyacrylate, polyacrylic acid. Calcium can be used.

  Moreover, the thicker the adhesive layer is, the greater the amount of water absorbed by adding the moisture absorbent, and the effect of suppressing moisture intrusion increases. However, it is not preferable that the laminate film is thick from the viewpoint of battery capacity. Therefore, by setting the thickness of the inner adhesive layer 25 in the range of 1 μm or more and 5 μm or less, both the effect of sticking the metal layer and the inner resin layer and the effect of suppressing moisture intrusion are achieved.

  The outer adhesive layer 24 for attaching the metal layer 21 and the outer resin layer 22 is positioned outside the metal layer 21 when the battery 20 is manufactured. That is, even if the moisture permeability is high, the metal layer does not block and moisture does not enter the battery. For this reason, although there is no particular problem even if the water absorbent is dispersed, it is better not to disperse the water absorbent from the viewpoint of adhesiveness and manufacturing cost.

  The battery element 10 is packaged using such a laminate film 17, and the periphery of the battery element 10 is welded to form a battery 20. The top portion of the battery from which the positive electrode terminal 15a and the negative electrode terminal 15b are derived usually has a welding width of about 2.5 mm in consideration of moisture intrusion. However, a narrower welding width can be achieved by using a moisture absorbent for the inner adhesive layer this time. Specifically, the welding width can be 0.5 mm or more and 2.5 mm or less.

  Here, the welding width is a width of a portion where CPPs which are the inner resin layers 23 are welded by heat being actually applied. In the case of a battery using a laminate film as an exterior, a cut burr may occur at the end of the laminate film when the laminate film is cut into a predetermined size, and the cut burr may be short-circuited with the metal terminal 25 in some cases. In addition, even if the cut burr is facing the outside of the battery or there is no cut burr, it is possible that the welding metal heater may short-circuit with the metal layer of the laminate film when pressure is applied to the end of the laminate film. . Then, the short circuit at the time of battery manufacture can be prevented by heat-welding the inner part which avoided the laminated film edge part.

  In this case, the cross-sectional view of the battery has a shape as shown in FIG. 5, but the welding width does not include a portion that has not been welded due to the avoidance of the metal heater. It is the width d where the resin layer is welded.

  Next, as shown in FIGS. 6A and 6B, portions on both sides (hereinafter referred to as side portions) 17b of the concave portion 17a in which the battery element 10 is accommodated are bent toward the concave portion 17a. The bending angle θ is preferably in the angle range of 80 degrees to 100 degrees. If it is less than 80 degrees, the side portions 17b provided on both sides of the concave portion 17a are too open, so the width of the nonaqueous electrolyte secondary battery 20 is widened. Therefore, it is difficult to reduce the size of the nonaqueous electrolyte secondary battery 20 and improve the battery capacity. Further, the upper limit value of 100 degrees is a value defined by the shape of the concave portion 17a. When the flat battery element 10 is accommodated, the limit value of the bending angle is about 100 degrees. In addition, the width | variety of the heat welding in the side part 17b becomes like this. Preferably it is chosen from the range of 0.5 mm-2.5 mm, More preferably, it is 1.5 mm-2.5 mm.

  Further, the folded width D of the side portion 17b is preferably set to be equal to or less than the height h of the concave portion 17a in order to reduce the size of the nonaqueous electrolyte secondary battery 20 and improve the battery capacity. Further, in order to reduce the size of the nonaqueous electrolyte secondary battery 20 and improve the battery capacity, the number of turns is preferably set to one.

  Moreover, although the above-mentioned embodiment demonstrated the nonaqueous electrolyte secondary battery 20 using the gel electrolyte, this invention is applicable also to the laminate film exterior battery using electrolyte solution. In this case, in the above-described embodiment, a step of applying the gel electrolyte to the positive electrode and the negative electrode surface is omitted, and a step of injecting the electrolytic solution in the middle of the laminate film welding step is provided.

  More specifically, after the three sides around the battery element are welded, an electrolytic solution is injected from the opening of the remaining one side, and then this one side is welded and sealed.

  Hereinafter, the present invention will be specifically described by way of examples. First, a battery element is produced.

[Production of positive electrode]
92% by weight of lithium cobaltate (LiCoO ₂ ), 3% by weight of powdered polyvinylidene fluoride, and 5% by weight of powdered graphite were uniformly mixed and dispersed in N-methylpyrrolidone to form a slurry-like positive electrode composite. An agent was prepared. This positive electrode mixture was uniformly applied to both surfaces of an Al foil serving as a positive electrode current collector, and dried under reduced pressure at 100 ° C. for 24 hours to form a positive electrode active material layer.

  Next, this was pressure-formed by a roll press machine to obtain a positive electrode sheet, and the positive electrode sheet was cut into a strip shape to form a positive electrode, and an Al ribbon lead was welded to an uncoated portion of the active material. In addition, polypropylene pieces were bonded to both sides of the portion of the lead sandwiched between the aluminum laminate films.

[Production of negative electrode]
Artificial graphite (91% by weight) and powdery polyvinylidene fluoride (9% by weight) were uniformly mixed and dispersed in N-methylpyrrolidone to prepare a slurry-like negative electrode mixture. Next, this negative electrode mixture was uniformly applied to both surfaces of a copper foil serving as a negative electrode current collector, and dried under reduced pressure at 120 ° C. for 24 hours to form a negative electrode active material layer.

  Next, this was pressure-formed by a roll press machine to obtain a negative electrode sheet, and the negative electrode sheet was cut into a strip shape to form a negative electrode, and a Ni ribbon lead was welded to the uncoated portion of the substance. In addition, a piece of polypropylene was bonded to both sides of the lead between the aluminum laminate films.

[Preparation of gel electrolyte]
A polyvinylidene fluoride copolymerized with 6.9% of hexafluoropropylene, a non-aqueous electrolyte, and dimethyl carbonate (DMC) as a diluting solvent are mixed, stirred and dissolved to obtain a sol electrolyte solution. Obtained. The electrolyte was prepared by mixing ethylene carbonate and propylene carbonate in a weight ratio of 6: 4 and dissolving 0.8 mol / kg LiPF ₆ and 0.2 mol / kg LiBF ₄ . The mixing ratio was a weight ratio of polyvinylidene fluoride: electrolyte: DMC = 1: 6: 12. Next, the obtained sol-form electrolyte solution was uniformly applied to both surfaces of the positive electrode and the negative electrode. Then, it was made to dry at 50 degreeC for 3 minute (s), the solvent was removed, and the gel electrolyte layer was formed on both surfaces of the positive electrode and the negative electrode.

  Next, a battery element was obtained by winding a belt-like positive electrode having a gel electrolyte layer formed on both sides and a belt-like negative electrode having a gel electrolyte layer formed on both surfaces in the longitudinal direction via a separator. . As the separator, a porous polyethylene film having a thickness of 10 μm and a porosity of 33% was used.

  The battery element produced as described above is covered with a laminate film, and the welding width is changed to produce a test battery having a thickness of 3 mm. At this time, a test battery is produced so that the outer dimensions do not change even if the welding width changes.

  Each test battery was charged with a constant current and a constant voltage of 800 mA and 4.2 V for 1 hour. Thereafter, constant current discharge at 800 mA was performed, and the process was terminated when the battery voltage reached 3.7V.

  Here, the following nine types of laminate films were used. These laminated films used aluminum having a thickness of 40 μm for the metal layer, nylon having a thickness of 25 μm for the outer resin layer, and CPP having a thickness of 30 μm for the inner resin layer. In addition, a moisture absorbent was added to the adhesive for adhering aluminum and CPP to 8 types, and only the adhesive was used for 1 type. As a moisture absorbent to be added, a laminate film A using sodium sulfate, a laminate film B using potassium sulfate, a laminate film C using magnesium sulfate, a laminate film D using calcium sulfate, A laminate film E using sodium polyacrylate, a laminate film F using potassium polyacrylate, a laminate film G using magnesium polyacrylate, and a laminate film using calcium polyacrylate A laminate film I was prepared using an adhesive that does not contain H or a moisture absorbent.

<Example 1>
For each of the cases where the above laminate films A to I were used, the welding width of the top portion was changed, and the test for Examples 1-1 to 1-24 and Comparative Examples 1-1 to 1-4 A battery was produced. Laminate films A to G were each made by adding 5% of a moisture absorbent to the adhesive, and the thickness of the inner adhesive layer between aluminum and CPP was 2 μm.

  Next, the produced test battery was stored for 7 days in an atmosphere at a temperature of 80 ° C. and a humidity of 90%, and the swollen amount after storage and the battery capacity after storage were measured. Table 1 below shows the type of laminate film used in each test battery, the weld width of the top portion, and the measurement results.

  From the above results, it can be seen that for the laminate film I to which no water absorbent is added, the battery swelling increases as the welding width decreases. This is because the amount of moisture intrusion is inversely proportional to the length of the infiltration path (welding width), and therefore, when no moisture absorbent is added, the amount of moisture intrusion into the battery is large and gas is generated due to the ingress of moisture. . Further, when the welding width is increased to 3.5 mm, the intrusion path length (welding width) is increased, so that it is possible to suppress the intrusion of moisture. The capacity will be reduced.

  On the other hand, when the laminate film A to the laminate film H to which the moisture additive is added is used, as shown in Examples 1-1 to 1-3, the battery bulge does not occur in the range where the welding width is 0.5 mm to 2.5 mm. It can be seen that the battery bulge is small even when the welding width is as narrow as 0.5 mm with no change of 0.2 mm.

  Further, as shown in Comparative Example 1-4, when the laminate film A is used and the welding width is set to 0.3 mm, the battery swell increases compared to Example 1-3 in which the welding width is set to 0.5 mm. Furthermore, when the welding width is increased to about 3.5 mm, it is considered that the volume of the battery element housing portion decreases as in Comparative Example 1-3, leading to a decrease in battery capacity. For this reason, when this invention is applied, by setting the welding width in the range of 0.5 mm to 2.5 mm, it is possible to obtain a battery that achieves both suppression of moisture intrusion and an increase in battery capacity.

<Example 2>
For each of the cases where the above laminate films A to I were used, test batteries of Examples 2-1 to 2-16 and Comparative Examples 2-1 to 2-5 were manufactured by changing the welding width of the side portion. . Laminate films A to G were each added with 5% moisture absorbent, and the thickness of the inner adhesive layer between aluminum and CPP was 2 μm. The welding width of the top part was 2.5 mm. Further, when the welded side part was folded back, the number of times of folding was set to 2 for some test batteries, and the number of times of folding was set to 1 for the remaining test batteries.

  Next, the produced test battery was stored for 7 days in an atmosphere at a temperature of 80 ° C. and a humidity of 90%, and the swollen amount after storage and the battery capacity after storage were measured. Table 2 below shows the type of laminate film used in each test battery, the welding width of the side portion, the number of times the side portion is folded, and the measurement results.

  From the above results, in the case of using the laminate film I to which no moisture absorbent is added, when the side portion is folded once, a relatively large battery swelling occurs even if the welding width is 2.5 mm. When the laminate films A to H to which the absorbent is added are used, battery swelling can be suppressed even if the side portion is folded once and the welding width is as narrow as 1.5 mm.

  In addition, when the laminate film I to which no moisture absorbent is added and the welding width is 5.0 mm and the side part is folded back twice, battery swelling is suppressed, but battery capacity is sacrificed, which is not preferable. This is because if the outer dimensions are constant, the volume of the battery element housing portion is reduced by a space that is folded twice.

  From Example 1 and Example 2 described above, by adding a moisture absorbent to the inner adhesive layer, it is possible to suppress moisture intrusion into the battery, and the welding width can be narrowed. Can be improved.

<Example 3>
In the laminate films A to H in which the water absorbing agent was mixed with the adhesive layer, the amount of the water absorbing agent added was changed, and Example 3-1 to Example 3-28 and Comparative Example 3-1 to Comparative Example 3- 2 test batteries were prepared. At this time, the test battery was tested with the weld width of the top portion being 1.5 mm, the weld width of the side portion being 2.5 mm, the side portion being folded once, and the thickness of the inner adhesive layer between the aluminum and the CPP being 2 μm. The battery was swollen and the battery capacity was measured.

  Next, the produced test battery was stored for 7 days in an atmosphere at a temperature of 80 ° C. and a humidity of 90%, and the swollen amount after storage and the battery capacity after storage were measured. Table 3 below shows the type of moisture absorbent used in each test battery, the amount of moisture absorbent added [%], and the measurement results.

  From the above results, it can be seen that battery swelling occurs when the amount of moisture absorbent added is small. This is considered because the effect of the moisture absorbent is small. On the other hand, if the amount added is too large, large battery swelling occurs. This is considered to be because the amount of moisture intrusion increases because the effect as an adhesive is reduced and peeling occurs at the welded portion. When using the laminate film A, it can be set as the laminate film which has a moisture permeation suppression effect and an adhesive effect by making the addition amount of potassium sulfate into 1% or more and 10% or less. It can also be seen that when other moisture absorbents are used, the laminate film can withstand practical use when the addition amount is in the range of 1% to 10%.

<Example 4>
In laminate films A to H in which a moisture absorbent was mixed in the adhesive layer, the thickness of the inner adhesive layer between aluminum and CPP was changed, and Example 4-1 to Example 4-24 and Comparative Example 4-1 to Comparative Example A test battery of Example 4-2 was prepared, and battery swelling and battery capacity were measured. At this time, a test battery was manufactured by setting the welding width of the top part to 1.5 mm, the welding width of the side part to 2.5 mm, and the side part to be folded once.

  Next, the produced test battery was stored for 7 days in an atmosphere at a temperature of 80 ° C. and a humidity of 90%, and the swollen amount after storage and the battery capacity after storage were measured. Table 4 below shows the type of laminate film used in each test battery, the thickness of the inner adhesive layer, and the measurement results.

  From the above results, when the laminate film A to which sodium sulfate is added as a moisture absorbent is used, large battery swelling occurs when the inner adhesive layer is as thin as 0.5 μm. This is considered to be because the effect as an adhesive layer is small and peeling occurs at the welded portion. In addition, when the inner adhesive layer is as thick as 7.0 μm, the adhesion performance is ensured and the battery swelling can be suppressed, but the infiltration of moisture itself cannot be completely suppressed. This is undesirable because it leads to an increase in moisture swell and a decrease in battery capacity.

  On the other hand, as in Example 4-1 to Example 4-3, when the inner resin layer is 1.0 μm to 5.0 mm, it can be seen that battery swelling can be suppressed and the battery capacity does not decrease. . In addition, as in Examples 4-4 to 4-24, when the laminate films B to H are used, the adhesive layer thickness is set to 1.0 μm to 5.0 mm. It can be seen that there is no decrease. For this reason, by setting the inner adhesive layer to 1 to 5 μm, it is possible to maintain the moisture penetration suppressing effect and the high battery capacity.

  The embodiment of the present invention has been specifically described above, but the present invention is not limited to the above-described embodiment, and various modifications based on the technical idea of the present invention are possible.

  For example, the numerical values and materials listed in the above-described embodiments are merely examples, and different numerical values and materials may be used as necessary.

  Further, the present invention can be applied to any battery using a laminate film exterior, and the shape of the battery element accommodated therein is not limited to the winding type.

It is a schematic diagram which shows the external appearance of the battery which used the laminate film as an exterior material. It is a schematic diagram which shows the structure of the nonaqueous electrolyte battery produced by applying this invention. It is a schematic diagram which shows the structure of the battery element accommodated in a nonaqueous electrolyte battery. It is sectional drawing which shows the structure of a laminate film. It is sectional drawing which shows the structure of the nonaqueous electrolyte battery produced by applying this invention. It is a schematic diagram which shows the structure of the nonaqueous electrolyte battery produced by applying this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Battery 2a ... Positive electrode terminal 2b ... Negative electrode terminal 3a, 3b ... Sealant 10 ... Battery element 11 ... Positive electrode 12 ... Negative electrode 13a, 13b ... Separator 14 ... Gel electrolyte 15a ... Positive electrode terminal 15b ... Negative electrode terminal 16a, 16b ... Sealant 17 ... Laminate film 17a ... Recessed part 17b ... Side part 20 ... Nonaqueous electrolyte secondary battery 21 ... Metal layer 22 ... Outer resin layer 23 ... Inner resin layer 24 ... Outer adhesive layer 25 ... Inner adhesive layer d ... Welding width θ ... Bending angle D ... Folding width h ・ ・ ・ Height of recess

Claims (4)

The battery element is housed in an exterior material made of a laminate film formed by adhering the outer resin layer and the inner resin layer to the both surfaces of the metal layer via the outer adhesive layer and the inner adhesive layer, respectively, and the above along the periphery of the battery element. In the nonaqueous electrolyte secondary battery in which the exterior material is sealed,
The metal layer is made of aluminum,
The inner adhesive layer is made of an adhesive in which a moisture absorbent is dispersed,
A non-aqueous electrolyte secondary battery, wherein a welding width of a metal terminal leading portion of the exterior material is 0.5 mm or more and 2.5 mm or less. The water absorbent is a sulfate represented by the general formula MSO ₄ or M ₂ SO ₄ (wherein M is selected from Na, K, Mg, Ca), or the general formula (—CH ₂ -CH (COOM)-) using at least one polyacrylate represented by _n (wherein M is selected from Na, K, Mg, Ca),
2. The nonaqueous electrolyte secondary battery according to claim 1, wherein an addition amount of the moisture absorbent is 1% or more and 10% or less of the adhesive.   The nonaqueous electrolyte secondary battery according to claim 1, wherein the inner adhesive layer has a thickness of 1 μm or more and 5 μm or less. The welding width of the side surface portion of the metal terminal lead-out portion of the exterior material is equal to or less than the battery thickness,
The side surface portion of the metal terminal lead-out portion is diffracted once in an angle range of 80 degrees or more and 100 degrees or less with respect to the welding surface so that side walls are formed on both sides of the battery element housed in the exterior material. The nonaqueous electrolyte secondary battery according to claim 1.

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